Oh Joy! More On The Younger Dryas

As an offshoot of my interest in Anthropogenic Global Warming, I have gradually developed an interest in the Younger Dryas Event, when something 13,000 years ago threw a slowly warming Northern Hemisphere back into glacial conditions for another thousand years. This, as an aside, is the event that served as model for the "climate tipping point" that causes so much trouble in The Day After Tomorrow. I've been particularly interested in the Younger Dryas Impact theory, which suggests that a comet exploding over the Laurentide ice sheet triggered the event. Although this theory seems to have been fairly thoroughly refuted.

In any case, the most common explanation of the event is that, as the ice-sheets retreated North, ice-dams holding in the Eastern edge of pro-glacial Lake Agazziz gave way and spewed vast amounts of cold water through the St. Lawrence river, where it caused a shut-down of the North Atlantic thermocline (sometimes called the great ocean conveyor) which carries warm water Northward via the Gulf Stream. This in turn caused Northern Hemisphere temperatures to plunge, glaciers to advance again, and so on and so forth.

Now, however, a new theory suggests a quite different route for this pulse of cold water. Instead of running East,

...geologists now believe they have found traces of this flood, revealing that cold water from North America's dwindling ice sheet poured into the Arctic Ocean, from where it ultimately disrupted climate-warming currents in the Atlantic.

In any case, you can read the whole thing through the link. As an aside, Nature, the magazine in which this new research was published, has just moved its news site outside of its pay wall. Lotsa fun there.

Comets Over Canada: Part II

Ever since Geophysicist Allen West and others put it forward last year, I've been interested in the theory that a comet or other ET object exploding somewhere over Canada might have been the event that ended the Clovis Culture, triggered the Younger Dryas, and brought about the demise of the Mammoths.

Evidence seems to be mounting in support of the theory, but the latest brick in the wall

Samples of diamonds, gold and silver that have been found in the [Ohio] region have been conclusively sourced through X-ray diffractometry in the lab of UC Professor of Geology Warren Huff back to the diamond fields region of Canada.

The only plausible scenario available now for explaining their presence this far south is the kind of cataclysmic explosive event described by West’s theory. "We believe this is the strongest evidence yet indicating a comet impact in that time period," says Tankersley.

...raised a few problems for me. I wrote:

I cannot get this to jibe with earlier articulations of the theory. Specifically, geophysicist Allen West has previously suggested that the impactor exploded before touching ground (a la the Tunguska Event), this to explain the absence of a crater. But how could diamonds originating in the Canadian diamond fields have turned up so far South if not as ejecta from a (still undiscovered) crater?

I fired off an e-mail re these concerns to some of the theory's architects, and yesterday Mr. West himself was kind enough to respond and address this point:

The hypothesis is fairly complex. We believe the impact was a collision with a cloud of debris, much like Comet LINEAR [see above left]. The smaller objects would have detonated in the atmosphere, much like Tunguska. Depending on the angle of entry, the largest objects could have impacted the 3-km-thick ice sheet, creating ice-walled craters that left no lasting imprint on bedrock.

There are multiple processes that could account for the diamonds: 1) some diamonds appear to have condensed inside burning biomass due to the heat and pressure of the impacts/airbursts; 2) diamonds are known form from shock impact upon terrestrial materials, such as coal, peat, carbonate rock, which would have been entrained as detritus in the ice sheet or would have been near the surface under the ice; 3) diamonds may have been formed by carbon vapor deposition (CVD) in the plasma of the fireball; 4) pre-existing kimberlite diamonds could have been ejected into the air along with other detritus entrained in the ice sheet; and 5) the impacts/airbursts most likely created immense meltwater surges both from above and below the ice and which would have carried pre-existing diamonds and other debris along with the meltwater.

Thank you Mr. West.

While I still had his ear, I asked Mr. West about my favorite part of the theory, where several of his co-workers had produced evidence that, at around the time of the onset of the Younger Dryas

mammoth[s] and other great beasts from the last ice age were blasted with material that came from space.

Eight tusks [...] all show signs of having being peppered with meteorite fragments.

In other words, when the comet crashed over Canada, its as though every mammoth in proximity to the event took a shotgun blast full of metal tiny pellets to the head!

Back in December, I put this part of the theory to the lads and lasses of the Dinosaur Mailing list. Gregory S. Paul gave it a thumbs down:

Some in this discussion still seem to imagine that sand sized blast debris can be imbedded in bone surfaces or skin at substantial range from an meteoritic explosion. Tiny particles can travel at high velocities if they are being carried along by air that is itself an equally fast moving part of the supersonic shock wave (shock waves are shock waves because they move faster than sound) produced by the explosion, which are limited to the region immediately surrounding the point source. Anything hit by high velocity microdebris in this zone will be so severely damaged by even more obvious shock and heat that the sand impact will be incidental. The supposedly impacted tusks and bones should be shattered and scorched. Any living animal will be killed outright, the debris will not be the killing agent. Once the micro-debris hits stable air it slowsdown to harmless terminal velocity in well under a kilometer. Even pebble sized objects will slow down to a 100 mph in a few kilometers. That is why being hit by a round musket ball or grape shot at long range was not lethal.

Dr. West was kind enough to respond to this as well:

Most discussions cite the usual explanation for impacts, which is true in most cases. However, that theory fails to explain the Carancas impact (http://www.universetoday.com/2008/03/18/peruvian-meteorite-may-rewrite-impact-theories/) or the particles in mammoth tusks. New research hints at a "tunneling" effect for some impactors, particularly fragmented ones. In those cases, the leading objects tunnel into the atmosphere and explode, apparently opening the way for trailing objects to reach ever closer to the surface. Some bunker-buster bombs work on the same principle. The first bomb opens a crater, the 2nd digs deeper, and subsequent ones even deeper.

In simulations, the initial explosions of a highly fragmented comet appear to be able to push aside the atmosphere and allow the particles from subsequent explosions to travel with almost no atmospheric friction. This is all theoretical but explains some seemingly inexplicable phenomena.

So there you have it!!!

Comets Over Canada

I have written here about the theory that the Younger Dryas, an 1,500 year long period of extreme cold that took place between about 13,000 and 11,500 years ago, was triggered by an "impact event" occurring somewhere over Canada. Well, more evidence in favor of this new theory has recently turned up:

Samples of diamonds, gold and silver that have been found in the region have been conclusively sourced through X-ray diffractometry in the lab of UC Professor of Geology Warren Huff back to the diamond fields region of Canada.

The only plausible scenario available now for explaining their presence this far south is the kind of cataclysmic explosive event described by West’s theory. "We believe this is the strongest evidence yet indicating a comet impact in that time period," says Tankersley.

Fascinating stuff. But I cannot get this to jibe with earlier articulations of the theory. Specifically, geophysicist Allen West has previously suggested that the impactor exploded before touching ground (a la the Tunguska Event), this to explain the absence of a crater. But how could diamonds originating in the Canadian diamond fields have turned up so far South if not as ejecta from a (still undiscovered) crater?

Pelted Mammoth

As I wrote here, there has recently been a new theory proposed to account for the onset of the Younger Dryas, a 1,500 year long period of extreme cold that took place between about 13,000 and 11,500 years ago. The new theory suggests that an "impact event" occurred somewhere near the Great Lakes at the beginning of the Younger Dryas:

Iridium peaks, and spikes of ammonium and nitrate which could have been produced by extensive burning of biomass, are also found in the Greenland ice cores. The authors therefore propose that the black horizon is the result of massive forest fires raging across the whole North American continent, triggered by the fiery impact of a meteorite or comet - or possibly a low altitude explosion like the Tunguska event. Enough soot from the fires, and dust from the impact, would have been thrown into the atmosphere to significantly cool the climate, causing enough environmental stress to wipe out both the Clovis people and the mammoths.

Well, now the same team of scientists behind this theory have found further evidence for arctic impacts:

Startling evidence has been found which shows mammoth and other great beasts from the last ice age were blasted with material that came from space.

Eight tusks dating to some 35,000 years ago all show signs of having being peppered with meteorite fragments.

Basically, and as the picture above shows, it looks like the poor animals took something like a shot-gun blast to the upper surface (but NOT the lower surface) of the tusks.

Of course the dates--35,000 vs. 13,000 years ago--don't really match up, which leads geoscience consultant Allen West to speculate that

Maybe, these were tusks from dead animals that were just exposed on the surface, so when this thing blew up in the atmosphere, it would have peppered them. The date could really be anywhere from 13,000 to 35-40,000 years ago.

Plus an excellent post by Loren Coleman at Cryptomundo describing how cryptozoologists got to certain aspects of this theory years ago.

The Younger Dryas, Celestial Impacts, and Scarborough Bluffs

When scientists, even pretend ones like Dennis Quaid in "The Day After Tomorrow", talk about Global Warming leading to a new Ice Age, they usually refer to the 1,500 year period between about 13,000 and 11,500 years ago, known as the Younger Dryas, as evidence. During this time the mean annual temperature, which had been gradually increasing for several thousand years, dropped suddenly to levels more typical of the Last Glacial Maximum (see graph above).

What caused the Younger Dryas? The conventional wisdom is that, as the planet gradually warmed and the glaciers retreated, proglacial lakes were formed by the water melting from them. The largest of these was Lake Agassiz, which is theorised to have been at the very center of the continent (around present day Lake Winnipeg). Another was Lake Algonquin, which comprised most of the current great lakes, Georgian Bay, and parts of Northern Michigan. And a third was Lake Iroquois, which was an enlarged version of Lake Ontario.

For most of its existence, drainage from Lake Agazziz was Southward into the proto-Mississippi. Lake Algonquin flowed South towards the Gulf of Mexico, and Lake Iroquois drained South into the Hudson River. However, as the glaciers retreated (so the story goes), the ice-dam which prevented water from these lakes from flowing Eastward collapsed abruptly. An immense pulse of cold, fresh water flowed down the St. Lawrence Valley and out into the Atlantic, where it caused a shut-down of the North Atlantic thermocline (sometimes called the great ocean conveyor) which carries warm water Northward via the Gulf Stream. This in turn caused Northern Hemisphere temperatures to plunge, glaciers to advance again, and so on and so forth.

If you live in the Greater Toronto Area you can actually find evidence of the aftermath of this ice dam collapse in the form of Scarborough Bluffs. These bluffs are made of packed clay soil and in fact constitute the shore-line of old Lake Iroquois; previous to the great Eastward outflow which drained all of these pro-glacial lakes, the waters stood about 100 feet higher than today.

However, a new theory has come onto the scene. A recent paper has suggested (backed by some pretty good evidence) that an "impact event" occurred somewhere near the Great Lakes at the beginning of the Younger Dryas:

Iridium peaks, and spikes of ammonium and nitrate which could have been produced by extensive burning of biomass, are also found in the Greenland ice cores. The authors therefore propose that the black horizon is the result of massive forest fires raging across the whole North American continent, triggered by the fiery impact of a meteorite or comet - or possibly a low altitude explosion like the Tunguska event. Enough soot from the fires, and dust from the impact, would have been thrown into the atmosphere to significantly cool the climate, causing enough environmental stress to wipe out both the Clovis people and the mammoths.

So did the cooling associated with this impact trigger the Younger Dryas? Probably not on its own. Though enough soot from the fires, and dust from the impact, would have been thrown into the atmosphere to significantly cool the climate, these effects would only have lasted several years. It is more likely that the impact caused a "destabilization/melting" of North America's interior ice sheets--including the bust up of that ice dam--which triggered that massive Eastward outflow from our pro-glacial lakes, and so on and so forth.

Now, why did I just write all this? Well, if you encounter a skeptic who tells you that its all bullshit because how can warming produce colder temperatures? you can tell them about the Younger Dryas. Of course, when scientists talk about the possibility of a Gulf Stream shut-down caused by modern day warming, they are looking at an entirely different mechanism: cold fresh water melting from the Greenland Ice Sheet, for the most part, bringing about the same effect.

Furthermore, and luckily enough, this outcome does NOT seem imminent.